Thermal transfer printing has displaced impact printing in many applications due to advantages such as relatively low noise levels during the printing operation. Thermal transfer printing is widely used in special applications such as in the printing of machine-readable bar codes and magnetic alphanumeric characters. The thermal transfer process provides great flexibility in generating images and allows for broad variations in style, size and color of the printed image. Representative documentation in the area of thermal printing includes the following patents:
U.S. Pat. No. 3,663,278, issued to J. H. Blose, et al. on May 16, 1972;
U.S. Pat. No. 4,315,643, issued to Y. Tokunaga, et al. on Feb. 16, 1982;
U.S. Pat. Nos. 4,628,000, 4,923,749, 5,128,308 and 5,248,652, issued to S. G. Talvalkar, et al.
U.S. Pat. No. 4,983,446, issued to Taniguchi, et al. on Jan. 8, 1991;
U.S. Pat. No. 4,988,563, issued to Wehr on Jan. 29,1991; and
U.S. Pat. No. 5,240,781, issued to Obatta, et al.
Most thermal transfer ribbons employ a synthetic resin as a substrate. Polyethylene terephthalate (PET) polyester is commonly used. The functional layer which transfers ink, also referred to as the thermal transfer layer, is positioned on one side of the substrate and a protective silicone back coat is typically positioned on the other side of the polyethylene terephthalate substrate to simplify passage under a thermal print head.
Many thermal transfer printer manufacturers specify that a silver reflective trailer must be attached to the end of the ribbon that trips a sensor to stop the printer for a ribbon change. Other manufacturers require a clear trailer wherein light is transmitted through the ribbon tripping a sensor and stopping the printer. A conventional reflective trailer is shown in FIG. 1, which is typically 20 inches in length. U.S. Pat. No. 4,985,292 describes alternative embodiments wherein end marks are printed on a portion of a thermal transfer ribbon either as a long continuous strip or in segments. U.S. Pat. No. 5,721,058 discloses methods of making sensor marks on a thermal transfer ribbon using thermally meltable ink.
Short length reflective segments have been used as markers in ribbons for impact printing such as typewriter ribbons. For example, U.S. Pat. No. 2,174,351 discloses the use of a band of aluminum paint applied to a typewriter ribbon to catch the eye of the operator and signal the end of the ribbon. U.S. Pat. Nos. 4,655,624 and 5,110,229 disclose the use of reflective aluminum sheets for use with photosensors to detect the end of a ribbon such as a typewriter ribbon. End of ribbon sensors for typewriter ribbons are also disclosed in U.S. Pat. Nos. 4,115,013, 4,146,388, 4,428,695 and 5,150,977. U.S. Pat. No. 4,401,394 discloses a universal end of ribbon sensing system for impact printing with ribbons having a reflecting tape segment and a clear transparent tape segment near its end.
Conventional thermal transfer ribbons may have a trailer positioned on an end thereof which is attached to the spool. The trailer has simple functions and there are many materials which will meet the physical property requirements necessary for the trailer to perform these simple functions. The materials used for the trailers of the thermal transfer ribbons may be identical to the substrate of the thermal transfer ribbon and so they can be synthetic resins such as polyethylene terephthalate (PET) polyester films. They can also be of a thickness greater than the polyester ribbon substrate (about 1 to 1.5 mil) so as to provide greater stiffness or they can be of a different material such as paper. These trailers can be adhered to one end of the polyester substrate with conventional pressure sensitive adhesive tape. The other end of these trailers is typically attached to the spool upon which the thermal transfer ribbon is stored with conventional pressure sensitive adhesive tape.